When running on the ground, an aircraft is generally steered by the wheel train mounted on the front or nose landing gear. This wheel train is fitted to the end of the telescopic leg of the landing gear and steering requires the end rod of the telescopic leg to be rotated, which end rod also slides axially relative to a strut which contains other apparatuses, including a shock absorber.
At present, there are two main types of solution for steering the nose wheel train, and which depend in part on the architecture of the landing gear. Landing gear normally includes a tubular strut which is the structural part hinged to the aircraft and which is tilting in order to retract and in order to lower the landing gear, and which has all of the driving members, braces, and locking members of the landing gear coupled thereto. The telescopic rod carrying the axle projects from this strut and co-operates with a shock absorber housed inside the strut.
In a first type of steering, the strut serves only to withstand forces, and in this case it is generally made of an aluminum alloy. In order to steer the wheels, this type of landing gear uses a tube between the strut and the rod, said tube being mounted to rotate inside the strut and being prevented from moving axially relative thereto in a position in which it projects from the strut. The rod then slides inside the tube while also being constrained to rotate therewith by means of an external scissor linkage mounted between the projecting portion of the tube and the portion of the rod which is close to the wheels. The portion of the rotary tube inside the strut is fixed to a toothed wheel which co-operates with a rack extending orthogonally to the axis of the tube and whose longitudinal displacements (as obtained, for example, by hydraulic means such as an actuator), cause the tube to rotate about its own axis inside the strut. This rotation is transmitted to the rod by the scissor linkage.
In a second type of steering, the strut may also contribute to guidance and shock absorbing for the rod. In this case, the strut is generally made of steel and the rod slides in it directly. In order to rotate the rod about its own axis, the mechanism used consists in a scissor linkage coupled between the portion of the rod which is close to the wheels and a ring which is mounted to rotate in an external groove on the strut. The ring includes external tabs each coupled to the rod of an actuator whose cylinder is hinged to a lateral extension on the strut. Thus the actuators rotate the ring and rotation of the ring is transmitted to the rod of the landed gear by the scissor linkage.
The present invention seeks to combine the respective advantages of these two prior steering mechanisms in an embodiment which is simple and cheap, i.e. using a strut made of aluminum alloy and independent actuators which are easily dismounted.